Utah-94-721002-System-Manual.pdf - 第153页

System Manual = lñÑçêÇ=fåëíêìãÉåíë=mä~ëã~= qÉÅÜåçäçÖó= mä~ëã~ä~Ä (c) For processes which deposit a combination of et ched material and mask layer, e.g. GaAs and sputtered photoresist during GaAs ‘via hole etchi ng’ it is…

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Arcing around the showerhead could be related to:
(a) Contamination of the showerhead / chamber walls (e.g. insulating/polymer coating,
backstreaming of pump oil or excessive use of vacuum grease on o-rings).
(b) A fault in the matching unit, more specifically the DC bias measurement circuit. Running at high
bias for extended periods can potentially cause damage to the DC bias measurement circuit which
can lead to a change in electrode performance and increased plasma potential causing sparking
on grounded walls. DC bias readings are also greatly reduced by this fault.
It may be worth manually scrubbing the showerhead and then trying again. If you are still seeing sparking
then it is worth investigating the matching unit.
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There are a number of plasma clean strategies currently in use:
(a) For
polymer processes (any process containing C
4
F
8
, CHF
3
, or CH
4
, e.g. C
4
F
8
/O
2
, CHF
3
/Ar, CH
4
/H
2
,
CHF
3
/Ar) we use an O
2
based etch to remove the polymer. The rate can often be increased by
adding 10-20% SF
6
, - this is more common in cleaning recipes for ICP chambers.
Typical examples are:
RIE chamber:
O
2
100 sccm
Pressure 100mT
Electrode 200 W
Time* 1-2 hours, but dependent on total process time since last clean
Period* After every 3-10hours etching
* These parameters are dependent on process gases, conditions and chamber wall temperature, so
are subject to change
ICP chamber:
O
2
40 sccm
SF
6
10 sccm (optional, if not available)
Pressure 20mT
ICP Power 1500 W
Electrode 150 W
Backside He 0 mbar
Time* 1-2 hours, but dependent on total process time since last clean
Period* After every 3 to 10 hours etching
* These parameters are dependent on process gases, conditions and chamber wall temperature, so
are subject to change.
(b) For processes which deposit an inorganic film, e.g. a-Si, SiO
2
, BO
x
etc from SiCl
4
, or BCl
3
it may be
necessary to use a more chemical process, e.g.:
SF
6
50 sccm
Pressure 20mT
ICP Power 1500 W
Electrode 150 W
Backside He 0 mbar
Process Information (Information contained in this document is confidential)
Issue 1: December 03 Page 10 of 30 Printed: 08 January 2006 09:37
System Manual= lñÑçêÇ=fåëíêìãÉåíë=mä~ëã~=qÉÅÜåçäçÖó= mä~ëã~ä~Ä
(c) For processes which deposit a combination of etched material and mask layer, e.g. GaAs and
sputtered photoresist during GaAs ‘via hole etching’ it is common to use a mixed Chlorine/fluorine
chemistry:
RIE chamber:
SF
6
85 sccm
Cl
2
50 sccm
Pressure 45mT
Power 150W
Temperature 20 C
Quartz carrier plate
ICP chamber:
Step1: 40sccm Cl
2
, 20sccm SF
6
, 50mT, 500W ICP, 200W RF, 22C, 0Torr He, 20mins to remove GaAs
and PR residues (may need to be longer after lots of ‘via hole etching’).
Step2: 50sccm O
2
, 20mT, 2000W ICP, 200W RF, 22C, 0Torr He, 30mins
Step3: 50sccm O
2
, 60mT, 2000W ICP, 200W RF, 22C, 0Torr He, 30mins
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It is quite a common requirement to process small samples or pieces of wafer. If the process requires
cooling to improve the etch profile or to allow use of resist mask at high power levels, then the small
pieces of wafer must be glued/fixed to a carrier wafer which is clamped and helium cooled. There are
several ways of attaching the small pieces of wafer to the carrier:
(a) Vacuum grease (after etching has been completed the vacuum grease can be removed from back
of wafer using IPA or acetone).
(b) Thermal compound.
(c) Photoresist (i.e. spin a few microns of resist onto a carrier wafer, place the sample on top while
the resist is still wet, push sample down well into resist, and then bake resist).
(d) Use a thermally conductive elastometer pad (see
EMI Shielding and Thermal Management Solutions).
With methods (a), (b) and (d) it is important that the sample completely covers the bonding material, so
that no bonding material is exposed to the plasma and therefore cannot be re-deposited on the wafer.
With all these methods it is necessary to also clamp the carrier wafer and apply helium pressure to the
back of the carrier wafer to provide cooling to the sample (there is no cooling effect simply from gluing
the sample to the carrier if there is no cooling of the carrier).
If the process does not need cooling (as with most low power RIE-only processes) then it is not necessary
to bond the sample to carrier. If the sample is liable to slide off the carrier during transfer, it is often
better to glue pieces of Si to the carrier wafer to act as locating pieces to hold the sample in place. This
avoids the need to glue the sample and therefore keeps the sample cleaner.
Process Information (Information contained in this document is confidential)
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mä~ëã~ä~Ä= lñÑçêÇ=fåëíêìãÉåíë=mä~ëã~=qÉÅÜåçäçÖó= System Manual
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For all systems with wafer clamping and helium backing for wafer temperature control. i.e. Plasmalab
System 100 with ICP 65, 180 and 380 sources. Also, occasionally RIE 133 systems and RIE 80 Plus.
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It is important to ensure that the helium is sealed adequately behind the wafer. If the helium is leaking
out past the wafer with a poor seal against the table, the thermal contact to the temperature-controlled
table will be degraded. The wafer will then heat up more than expected and the process results may
suffer. For example, in SiO
2
etching the profile may become partially isotropic and/or any photoresist
masking used may burn too easily.
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(a) If the wafer is sealing the helium effectively, the measured He flow will be less than that when no
wafer is present.
(b) Set a range of He pressures and note the measured helium flows with no wafer loaded. (Set all
process gases, RF and pressure to zero and work in ‘manual’ mode.)
(c) Load a blank Si wafer of the correct size (if the system is a standard single wafer type) and note
the He flows for the same range of set He pressures.
(d) Load a typical customer wafer (e.g. with a thick SiO
2
layer) and note the He flows for the same
range of set He pressures. If a carrier is appropriate for the system, use that.
(e) Fill results in the following table. (If you do not have the capability to measure Helium flow then
measure CM gauge chamber pressure with APC fully open, no other gases flowing).
Set He/Torr He flow/sccm
No wafer
He flow/sccm
Si wafer
He flow/sccm
Customer wafer
7
10
15
20
(f) The larger the difference between ‘No wafer’ and ‘With wafer’ flows, the better the seal. ‘With
wafer’ values should be less. Pass criteria are still being evaluated but a recent example with
acceptable results is as follows.
(g) Recent acceptable example:
Set He pressure No wafer He flow With wafer He flow*
7Torr 4.2sccm <3.9sccm
10Torr 7.2sccm <6.5sccm
*These were the maximum values observed (usually occurring for wafers with thick SiO
2
layers)
and cooling was thought to be adequate because profiles were acceptable.
If there is little or no difference between the ‘No wafer’ and ‘with wafer’ flows, then the seal is
ineffective.
Process Information (Information contained in this document is confidential)
Issue 1: December 03 Page 12 of 30 Printed: 08 January 2006 09:37